Optically variable devices (“OVD”) are optical devices, which diffract, refract, transmit, absorb, or scatter light and whose optical properties can vary within that device. Some examples of OVD would be holographic films, holograms, including: reflection holograms, absorption holograms and polarization holograms, diffraction gratings, embossed films, original artwork, embossing rolls, and replicas. Optically variable media (“OVM”) are optical media, which diffract, refract, transmit, absorb, or scatter light and whose optical properties can vary within that device. Some examples of OVM which can be used to make OVD would be polymers, polymer films, multilayer films, films with inclusions, films with embossing layers, photoresist, epoxies, silicones, lacquers, cellulose triacetate, glasses, and optical materials. Exemplary polymers include: polypropylene, ethylene propylene copolymers, ethylene propylene butene terpolymers, propylene butene copolymers, blends of polypropylene and propylene copolymers, polyetheretherketone, polyimide, polyamide, polysulfone, polyphenylene sulphide, polyamideimide, polyethersulphone, polyetherimide, polyphenylsulphone, polycarbonate, polyacrylate, including polymethacrylate homopolymers and copolymers, polyester, epoxy-based polymers, polysiloxane.
An example of holographic or optically variable devices can be found in U.S. Pat. No. 5,032,003, and in U.S. Pat. Pub. No. US 2005/0112472 A1. An example of holographic or optically variable materials can be found in U.S. Pat. No. 5,781,316 and U.S. Pat. Pub. No. US 2004/0101982 A1. These references are incorporated by reference.
The optical quality of OVD or OVM means the optical properties, which are measured by the method proposed here, and that relate directly to the “optimum” or “best” values that are attainable based on understanding of the underlying physics. For example, the diffraction efficiency of an OVD or OVM can be measured and compared to the best possible value that is attainable based on the understanding of the underlying physics. The underlying physics in this case might be the “optimum” or “best” values of the period and depth of the grating that is embossed on the surface.
The optical characteristics of OVD or OVM means the optical properties, which are measured by the method proposed here, and that relate directly to the “desired” or “target” values that are attainable based on specific applications or customer requirements. For example, the diffraction efficiency of an OVD or OVM can be measured and compared to the “desired” or “target” values that a customer requires. This information could be used to control a manufacturing process to produce the desired OVD or OVM or to set quality standards.
The visual appearance of OVD or OVM means the optical properties, which are measured by the method proposed here, and that relate directly to the “perceived visual effect” that is desired by a customer, artwork designer, or process control person. For example, the diffraction efficiency of an OVD or OVM that is found to be desirable due to its “perceived visual effect” can be controlled in the manufacturing process. In addition, an artwork designer could produce original artwork, which utilizes this desirable “perceived visual effect”.
Assessment of the optical quality of holographic films and artwork is currently entirely subjective. A need exists for practical methods of making objective quantitative assessments of quality of optically variable devices and optically variable media. Such methods must produce repeatable results and provide standards by which media can be reliably evaluated. Such methods would be useful in assessing new designs of OVD and OVM, provide standard for assessing the quality of purchased devices and for quality control in the production of OVD and OVM. The application of these methods would therefore result in (a) reduced manufacturing costs (b) improved film quality and consistency and (c) an improved capability to match customer requirements.